Article Figures & Data
Figures
- Figure 1.
Identification of precerebellar neurons in pons and medulla via retrograde labeling of red fluorescent dextrans. A, Tracer injection site (red) in the floccular lobe of the cerebellum is shown in a coronal section ∼5.6 mm caudal to bregma. Retrogradely labeled neurons from this injection are shown in coronal sections in B–E. B, Section through the caudal medulla, ∼7.75 mm caudal to bregma, showing neurons in the inferior olive (dorsal cap) that were retrogradely labeled from the cerebellar flocculus. C–E, Retrogradely labeled neurons in the MVN, NPH, nucleus of Roller/nucleus intercalatus, and supragenual nucleus in medullary sections 6.96, 6.5, and 5.8 mm caudal to bregma, respectively. F, A second example of a cerebellar injection, ∼6.25 mm caudal to bregma, which resulted in the pattern of retrograde labeling show in G–J. G, Retrogradely labeled neurons in several portions of the inferior olive, as well as in the LRN, are shown in this medullary section ∼7.56 mm caudal to bregma. H, Retrogradely labeled neurons in the LRN, ∼7.76 mm caudal to bregma. I, Retrogradely labeled neurons in the external cuneate, adjacent to the fourth ventricle in this section, ∼7.35 mm caudal to bregma. J, Retrogradely labeled neurons in the NRTP and the pontine nuclei in a section ∼4.25 mm caudal to bregma. Scale bars: (in F) A, F, 500 μm; (in G) B–E, H–J, 100 μm.
- Figure 2.
Action potential profiles of mossy fiber neurons in eight precerebellar nuclei are similar. A, Average action potential waveform from eight retrogradely labeled neurons recorded in the external cuneate, lateral reticular, medial vestibular, prepositus hypoglossi, reticular tegmenti pontis, pontine, Roller, and supragenual nuclei. B, Action potential width at half-height for all recorded neurons. C, AHP amplitude for all recorded neurons. E, External cuneate nucleus; L, lateral reticular nucleus; M, medial vestibular nucleus; N, nucleus prepositus hypoglossi; T, nucleus reticularis tegmenti pontis; P, pontine nucleus; R, nucleus of Roller/nucleus intercalatus; S, supragenual nucleus. Open symbols are individual data points. Black horizontal bars represent the median value for each nucleus.
- Figure 3.
Precerebellar neurons transform input current into firing rate linearly. A, Instantaneous firing rate versus time for a retrogradely labeled neuron recorded in the NRTP in response to 1 s depolarizing inputs of increasing magnitude. B, The relationship between current and mean firing rate across 1 s depolarizing steps for the neuron shown in A. Lines represent best linear fits to firing rate responses below and above 80 spikes per second. C, Maximum firing rates for all recorded precerebellar neurons. D, Linear correlation coefficient (R2) for current-to-firing rate relationship below 80 spikes per second. E, Gain of the current-to-firing rate relationship below 80 spikes per second. Significant differences of p < 0.05 were found for L versus M or S, and R versus M, N, or S. F, Ratio of gain for the current-to-firing rate relationship under and over 80 spikes per second. F, Ratio of gain for the current-to-firing rate relationship below and above 80 spikes per second. G, Adaptation ratio indicates the ratio of the firing rate at the end versus the start of the 1 s current step measured at steady-state firing rates of 150 spikes per second. H, Input resistance measured below spike threshold. E, External cuneate; L, lateral reticular nucleus; M, medial vestibular nucleus; N, nucleus prepositus hypoglossi; T, nucleus reticularis tegmenti pontis; P, pontine nucleus; R, nucleus of Roller/nucleus intercalatus; S, supragenual nucleus. Open symbols are individual data points. Black horizontal bars represent the median value for each nucleus.
- Figure 4.
Mossy fiber neuron firing rate modulation in response to sinusoidal inputs. A, Top trace, Voltage recording of a mossy fiber neuron firing during sinusoidal modulation. Middle trace, Firing rate of the neuron. Bottom trace, Sinusoidal current input to the soma. B, C, Bode plots summary of gain (B) and phase (C) in mossy fiber neurons. Symbols represent the average response of neurons in the eight precerebellar nuclei. Error bars indicate SEM. ExCun, External cuneate; Roller, nucleus of Roller/nucleus intercalatus; Supragen, supragenual nucleus.
- Figure 5.
SK channels constrain the gain and maximum firing rate of mossy fiber neurons. A, Example of an action potential before and after application of apamin (50 nm), a blocker of SK channels, in a precerebellar neuron recorded in the lateral reticular nucleus. B, Instantaneous firing rate versus time during a 1 s depolarizing current step before and after application of apamin. C, Relationship between current and mean firing rate over 1 s depolarizing steps before (open circles) and after (filled triangles) apamin application. D, E, Differences in AHP amplitude (D) and adaptation ratio (E) after apamin perfusion. Changes in gain below 80 spikes per second (F) and maximum firing rate and maximum current input (G) after apamin, normalized to control values. D–G show results from precerebellar neurons recorded in the LRN (n = 3), pons (n = 1), NRTP (n = 4), and nucleus of Roller (n = 2).
- Figure 6.
BK and Kv3 currents contribute to gain and maximum firing rates of mossy fiber neurons. A, Example of an action potential before and after application of paxilline (l μm) and paxilline plus TEA (l μm and 1 mm, respectively) in a precerebellar neuron recorded in the nucleus of Roller. B, Instantaneous firing rate versus time during a 1 s depolarizing current step before and after application of paxilline and paxilline plus TEA. C, Relationship between current and mean firing rate over 1 s depolarizing steps before and after paxilline and paxilline/TEA application. D–F, Change in gain below 80 spikes per second (D), maximum input (E), and maximum firing rate (F) normalized to the control values. G, Change in AHP amplitude after paxilline and paxilline/TEA exposure. D–G show results of paxilline and TEA on precerebellar neurons recorded in each of the eight precerebellar nuclei analyzed in this manuscript (2 neurons each from NPH and the nucleus of Roller).
- Figure 7.
Postinhibitory rebound firing and the effect of IH blockade varies across and within precerebellar nuclei. A1, Example of firing responses to a 1 s hyperpolarization in a precerebellar neuron recorded in the lateral reticular nucleus. A2, Same neuron as in A1 after application of the IH blocker ZD7288 (50 μm). B1, Firing responses to hyperpolarizing inputs in a second exemplar, recorded in the external cuneate. B2, Same neuron as in A1 after application of the IH blocker ZD7288 (50 μm). Neurons were maintained at baseline firing rates of 10 spikes per second with DC current. C, Peak rebound firing rate (baseline subtracted) for all precerebellar neurons recorded. Significant differences (p < 0.05) are P versus L, M, N, R, or S, and T versus R. D, Delay from hyperpolarization offset to the next spike in all precerebellar neurons recorded. E, Peak rebound firing rate after IH blockade with ZD7288 is plotted versus the control rebound rate for precerebellar neurons recorded in the external cuneate nucleus (n = 3), nucleus of Roller (n = 5), NRTP (n = 2), and LRN and pontine nuclei (n = 1 each). Two neurons in the external cuneate with rebound firing rates of >50 spikes per second are not shown. The diagonal line represents no change. F, Delay to first posthyperpolarization spike after ZD7288 is plotted versus control delay for the same precerebellar neurons plotted in E. E, External cuneate nucleus; L, lateral reticular nucleus; M, medial vestibular nucleus; N, nucleus prepositus hypoglossi; T, nucleus reticularis tegmenti pontis; P, pontine nucleus; R, nucleus of Roller/nucleus intercalatus; S, supragenual nucleus.
Tables
Nucleus n # firing spont. Spont. FR ± SE (spikes/s) Vrest ± SE (mV) External cuneate 24 5 22 ± 8 −75.6 ± 1.2 LRN 13 4 8 ± 2 −66.8 ± 1.6 MVN 40 21 13 ± 2 −71.4 ± 1.1 NPH 21 6 11 ± 7 −74 ± 1.3 NRTP 30 1 9 −76 ± 1.0 Pontine 20 0 NA −78 ± 1.6 Roller 27 8 16 ± 4 −72 ± 1.7 Supragenual 23 4 12 ± 2 −73 ± 1.3 Vrest indicates resting membrane potential of neurons that did not fire spontaneously. Spont., Spontaneously; NA, not applicable; FR, firing rate.
- Table 2.
Comparisons of intrinsic excitability in neurons projecting to the cerebellum, oculomotor nucleus, and reticular formation
Precerebellar median (1st and 3rd quartiles), n OMN-projecting median (1st and 3rd quartiles), n Reticular-projecting median (1st and 3rd quartiles), n p value Max firing rate 164 (123, 237), 170 316 (248, 405), 37 244 (154, 336), 33 <0.0001 0.0016 Adaptation index 0.81 (0.77, 0.86), 150 0.88 (0.86, 0.9), 37 0.86 (0.82, 0.88), 30 <0.0001 0.0022 Gain 83 (56, 103), 150 188 (149, 221), 37 123 (101, 137), 30 <0.0001 <0.0001 Values are the median and 1st and 3rd quartiles. Gain values are reported for evoked firing rates of >80 spikes per second. Statistical significance was determined with a nonparametric Wilcoxon sign rank test and is reported for precerebellar versus oculomotor nucleus (OMN) and reticular projecting neurons, respectively. Data for neurons projecting to the OMN and reticular formation were from Sekirnjak and du Lac (2006) and Kolkman et al (2011), respectively.
